Scroll-type fluid compressors are well known in the prior art. U.S. Pat. No. 4,432,708 issued to Hiraga et al discloses an apparatus including two scrolls, each having a circular end plate and a spiral element disposed on each plate. The scrolls are equally offset such that both spiral elements cooperate to make a plurality of line contacts between their spiral curved surfaces.
In operation, one of the scrolls is subjected to an orbital motion and the line contacts shift, resulting in a change in the volume of the fluid pockets contained within the scrolls. This change in volume of the fluid pockets is utilized to compress fluids, for example, air conditioning refrigerants needed for operation of air conditioning systems in automobiles.
Compliant devices of various construction have been designed into scroll-type compressors of the prior art. Scroll-type compressors intended for automotive use include compliant devices to overcome disadvantages associated with compressor operation in general. It is known in the art that an air conditioning compressor generally requires the greatest driving power during start-up. Thus, if the compressor is connected to a driving power source, for example, an internal combustion engine of an automobile, a significant load is imposed on the engine during compressor start-up. Compliant devices are utilized to reduce start-up torque requirements supplied by the compressor driving power source to the compressor.
In addition, a condition called "slugging" is detrimental to the internal components of scroll-type air conditioning compressors. Slugging occurs when fluid refrigerant used in the air conditioning system condenses into a liquid. This condition exists when the automobile is subjected to cold temperatures during the winter months and during large temperature deviations such as in day/night cycles in desert areas. The refrigerant in the gaseous state tends to migrate into the lower temperature areas of the internal components of the compressor. Specifically, the refrigerant in the gaseous state condenses in the cavities formed within the two interfitting scrolls.
Operation with the refrigerant in a condensed or liquid state is detrimental to the internal components of the air conditioning compressor because the compressor is designed to compress only fluids in a gaseous form, not fluids in liquid form. Attempted compression of liquid refrigerants may stress or deform various internal compressor components and sometimes disables the compressor entirely.
U.S. Pat. No. 4,580,956 to Takahashi et al. discloses a scroll-type fluid compressor including a compliant device. The apparatus comprises a housing, a fixed fluid displacement member and an orbiting fluid displacement member. Upon startup, a spring pushes an orbiting fluid displacement member in a direction which reduces its orbital radius. Thus, the spring acts as a compliant, or restriction device which operates to separate the line contacts between a fixed member and the orbiting member until the orbiting member reaches a predetermined rotational frequency.
The predetermined rotational frequency is set such that the compressor starts in an unloaded condition and eventually progresses to a fully operational condition. The compliant device in the Takahashi patent displaces the revolutional axis of the support bushing, thereby displacing the revolutional axis of the orbiting scroll. This displacement separates the line contacts between the orbiting and fixed scrolls and hinders compression during start-up within the apparatus. However, the Takahashi compliant device is expensive to manufacture and assemble in mass production. In addition, it includes various mechanical components that will over time fail.
European Patent No. 270917 discloses another compliant device comprised of a disc shaped rotor with an aperture eccentric to the outer casing of the rotor for accommodating a shaft. A rubber substance is used to fill the intervening space between the aperture and the casing for absorbing various forces applied upon the aperture during rotation of the disc rotor.